Projectile-weapon aiming systems are discussed herein principally in the context of telescopic sights rigidly affixed to a weapon and commonly embodied as a riflescope. Riflescopes include reticles for aiming at locations indicated by a reticle aiming mark. A reticle aiming mark defines an aiming point at which a straight aiming line of sight intersects at a discrete distance (so-called range or target distance) a bullet or other projectile's curved trajectory. The curved trajectory is traversed by the projectile falling and decelerating while traveling from the weapon to the target location, and it depends on ballistic characteristics, such as projectile weight, drag, and initial velocity (e.g., muzzle velocity), and on other factors impacting external ballistics of an ammunition. Thus, the projectile, due to its curved trajectory, will intersect the aiming line of sight at one range and pass below or above it at other ranges. This necessitates the use of elevation adjustments to adjust the aiming line of sight for intersecting the curved trajectory at another target range.
Elevation adjustments in riflescopes are typically made by turning an adjustment mechanism of the riflescope to impart vertical movement of optical elements (as described, for example, in U.S. Pat. No. 3,297,389 of Gibson) or of the reticle (as described, for example, in U.S. Pat. No. 3,058,391 of Leupold), so that the aiming line of sight is accurately sighted-in at the range of the target. To adjust for the effect of crosswinds, riflescopes also typically include a separate adjustment mechanism for imparting horizontal movement to the optical elements or reticle. In yet other projectile-weapon aiming systems, the entire aiming device is adjusted relative to the weapon via an adjustable sight mount. In each type of adjustment device, adjustment of the elevation and windage is time consuming and may require the shooter to take his or her eyes off the target while manipulating the adjustment mechanisms.
There have been proposed numerous reticles and riflescopes designed to provide the shooter with a plurality of aiming marks for shooting at targets at various predetermined ranges, i.e., aiming marks producing line of sight/trajectory intersections at various target distances. Some of these include devices for approximating the range to the target. These riflescopes propose to eliminate the need to make elevation adjustments in the riflescope to compensate for bullet drop at different ranges. Instead, the shooter merely aims with one of several holdover aiming marks on the reticle spaced below the primary crosshair. Example riflescopes employing reticles to facilitate “holdover aiming” are described in U.S. Pat. No. 3,190,003 of O'Brien; U.S. Pat. No. 1,190,121 of Critchett; U.S. Pat. No. 3,392,450 of Herter et al.; U.S. Pat. Nos. 3,431,652 and 3,492,733 of Leatherwood; U.S. Pat. No. 6,032,374 of Sammut; U.S. Pat. No. 6,591,537 of Smith; U.S. Pat. No. 7,185,455 of Zaderey; and U.S. Pat. No. 7,603,804 of Zaderey et al. Most of these patents propose riflescopes providing a plurality of range-related aiming marks accompanied with aiming mark selection devices, the use of which depends on relative height of the image of a target of known or estimable height compared to the height of a feature in the reticle. These reticles are also designed with a single set of aiming marks corresponding to a single type of ammunition at a time. Shooting another type of ammunition having different ballistic characteristics necessitates adjustment of the optics or reticle.
U.S. Pat. No. 6,032,374 of Sammut and U.S. Pat. No. 6,591,537 of Smith propose reticles having a series of secondary aiming marks spaced below a primary aiming mark at predetermined intervals for compensating for bullet drop. These secondary aiming marks provide holdover aiming points, which the shooter selects based on the secondary aiming mark that most closely corresponds to the observed range. The secondary aiming marks of Sammut are evenly spaced, but a bullet's trajectory is parabolic, so Sammut requires preliminary collection of ballistic data to determine the range corresponding to each secondary aiming mark. The corresponding ranges determined by the collection of ballistic data are applicable only for the ballistics of particular ammunition for which data is collected. Furthermore, a shooter must either memorize the ranges that are empirically determined for various types of ammunition having different ballistic characteristics or refer to a worksheet where the ballistic data and corresponding ranges have been recorded.
Smith purports to provide secondary aiming marks for regular incremental ranges (typically 300, 400, 500, and 600 yards) in an attempt to eliminate the need, as with the device of Sammut, to refer to ballistics data or to memorize the ranges corresponding to the secondary aiming marks. However, the ranges of the secondary aiming marks of Smith are accurate only for a particular predetermined rifle and ammunition combination, referred to as the “ballistic factor.” For ammunition having a ballistic factor different from the factor for which the reticle is designed, Smith proposes to apply a decal to the stock of the rifle or some other convenient location for reference in determining the irregular ranges at which the secondary aiming marks are to be used to aim the rifle.
U.S. Pat. No. 4,403,421 of Shepherd describes a two-reticle system including crosshairs located at a rear focal plane of a riflescope, and a secondary reticle located at the front focal plane and made of a polygonal-shaped transparent material. The secondary reticle is mounted in a manually rotatable mounting, to allow the reticle to be moved in and out of the field of view, and to allow the polygon to be rotated so that different reticle patterns on each of its faces are viewable. Shepherd describes that the secondary reticle may have different sets of range indicia marked on different faces of the reticle, in which the different sets of range indicia correspond to different families of bullets or different weights of bullets having different muzzle velocities. The different range scales are not simultaneously visible and require the user to rotate the reticle to select from the different patterns.
Several other patents for devices commonly referred to as autoscopes describe electronically controlled reticles having aiming marks that are displayed on an electronic display to correspond to a particular selected ammunition and range data. U.S. Pat. No. 6,269,581 of Groh is one example.